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Temperature: A Hot Issue For Wine

Heavy snow has been a feature of this winter's extreme conditions; a container ship being unloaded in China
© AFP | Heavy snow has been a feature of this winter's extreme conditions; a container ship being unloaded in China
Bushfires in Australia; blizzards in the northeastern United States. Shipping wine in extreme temperatures is more of an issue than ever, and may present a bigger problem than corked or counterfeit wine.

During a recent cold snap, I backed out of the garage, put wine bottles in and around the car, and then went back inside to sit by the fire. All in the name of experimentation, you understand. I was curious to learn if the lows of 20°F (–6°C) overnight would freeze wine in the bottle.

Even if consumers don’t store their wines outside, wine retailers continue to ship wine in the winter and distributors make deliveries to shops and restaurants every weekday. In order to simulate these conditions, I placed one bottle in a Styrofoam shipping box and another just loose in the body of the car (some distributors load their trucks the evening before, leaving the wine in them overnight). For good measure, I placed a bottle in a snow bank for the maximum chill.

When I returned in the morning, a water bottle inadvertently left in the car had frozen solid, but none of the wines had. Even the wine in the snow bank was still in good shape.

It turns out that because wine is only about 86 percent water, the remaining ethanol (which freezes at –173­°F (–114°C) lowers the actual freezing temperature of wine below 32°F (0°C). Indeed, producers intentionally bring white wines down to around 32°F during winemaking, a process known as cold stabilization. This makes tartaric acid crystallize and fall to the bottom of the tank. If the winery didn’t do this preemptively, these harmless 'diamonds' could precipitate in the bottle if consumers or restaurants aggressively chilled the bottles.

Below about 20°F, wines run the risk of having the water volume start to turn slushy, if not solid. For a red wine that hasn’t undergone cold stabilization, the crystallization could occur, as well as precipitation of tannins or other polyphenols that contribute to the taste and ageability of the wine. At that temperature, either reds or whites could compromise the cork because of a change in volume in the bottle. Without a good seal, the wine could be exposed to air, hastening oxidation.

The effects of the flip side of extreme cold – extreme heat – are better known to wine enthusiasts because they are so much more prevalent and damaging. Think of a wine left outside in a loading bay in the summer sun. It browns quickly, has reduced flavors, and tastes a lot older than it should. It is cooked.

But what’s not widely known is just how much wine is exposed to extreme heat on the journey from the winery to the consumer. Even if an importer ships via refrigerated containers, local distributors do not uniformly use climate-controlled warehouses (although many do) and there are still some who deliver the proverbial last mile in a truck without refrigeration. And even overnight airfreight could subject wine to extreme heat while out for local delivery.

L-R: Wine barrels pictured during the cold stabilization process; data showing temperature fluctations during shipments of wine
© Agne27/eProvenance | L-R: Wine barrels pictured during the cold stabilization process; data showing temperature fluctations during shipments of wine

The Boston-based company eProvenance has collected more than one million data points on more than 5,000 actual wine shipments around the world. Its data shows that about 15 percent of shipments are exposed to extreme heat (86°F or 30°C). Shipments to China demonstrate the highest amount of exposure to heat, with fully 47 percent of shipments breaching 86°F. On the route from France to China, a staggering 90 percent touched that level. 

eProvenance undertook a study with ETS Laboratories in Napa, and found that a wine exposed to 80°F (27°C) for 36 hours showed permanent change in its chemical structure. At 86°F, only 18 hours' exposure had the same withering effects. This makes cooked wine the biggest threat that wine consumers face, far greater than “corked” wine or counterfeit wine.

eProvenance clients also collect geolocation data so they can take corrective action. And with provenance zealot Laurent Ponsot, of Domaine Ponsot, and London's patrician wine shop Berry, Bros & Rudd now using the system, there’s hope that one day the consumer may see the data on each bottle before purchase.

Since wines with superior provenance fetch a premium in the marketplace, eProvenance is seeking to make shipping temperature more a part of the discussion and understanding of provenance. And rightfully so: if asparagus and fresh-cut flowers can be zipped around the world in cold, why not fine wine?

For my wine purchases, I would feel most confident about avoiding extreme temperatures by having wine shipped to me starting late fall through to the spring (on all but the coldest days of winter). If I wanted to really reduce my risk of cooked wine and wasn’t buying from an importer and retailer that maintains cool temperatures, I would drastically cut back purchases from summer through the fall, even in stores.

But that’s impractical. The best approach would be simply to know if the wine had been exposed to heat, because then I could be confident buying all year round. With the technology now available, hopefully this isn’t too far away from becoming reality.

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